Two motor hoist control



Jan. 12, 1960 L. J. SRNKA TWQMOTOR HOIS'I CONTROL Filled Sept. 18, 1958 3 Sheets-Sheet 1 INVENTOR. M M BY NPR as n lH Wm: IT- ma NJ A $5 3 N5 wig 2s 28 iJ uokmad u wzkfiwduulq $2.6 :20 3

g Twy 55d Jan. 12, 1960 SRNKA TWO MQTOR HOIST CONTROL 3 Sheets-Sheet 2 Filed Sept. 18, 1958 Jan. 12, 1960 L. J. SRNKA 2,920,776

TWO MOTOR HOIST CONTROL Filed Sept. 18, 1958 3 Sheets-Sheet 5 x" DENOTES CONTACT CLO5ED 1N VENT OR.

' spective motor. Since these motors TWO MOTOR HOIST CONTROL Leonard J. Srnka, Garfield Heights, Ohio, assignor to Square D Company, Detroit, Mich., a corporation of Michigan p Application September 18, 1958, Serial No. 761,762

15 Claims. (Cl. 214656) The present invention relates to a control system for controlling a plurality of motors in such manner that the rotors may be rotated independently of each other and may be rotated in synchronism with each other, and

more in particular to a control system wherein the hoist line and closing line motors of a two bucket hoist may be simultaneously and'cooperatively or independently controlled from a single master switch to hoist the bucket and to lower the bucket while maintaining it in a single attitude, for example, open.

The present invention is adaptable for use in hoisting applications wherein it is desired to use at least two lines, each having its own motor, for hoisting and lowering loads and particularly for lowering a load at high rates of speed while maintaining it in a single attitude. For the purpose of better understanding, the invention will hereafter be described in the application of a two line bucket type hoist.

In bucket hoists commonly used in the industry, a clam shell type bucket is usually suspended from a hoist support or trolley by a closing line and a holding line. The closing line is attached to the hinge of the bucket and the holding line usually is attached to one of the shells of the bucket at a distance from the hinge. By proper manipulation of these lines relative to each other, it is convenient for the hoist operator to open and close the bucket and to hoist and lower it. Generally each line is wound on its own drum, which is driven by its remust be operated in a coordinated relationship which includes a simultaneous operation of both motors as well as the independent operation of one motor relative to the other, in the past it was found necessary to provide each motor with its own independent motor control circuits. This meant that each motor control system had to have its own master switch. It has long been recognized that if the master switches in each of the motor control systems could be combined into a single master switch the hoist would be much easier for-the operator to control.

Another problem encountered with the prior hoist was controlling the closing line and holding line motors so that they would operate cooperatively and in synchronism during lowering of the bucket into a pile of dirt or other material in such manner that the bucket would maintain a single attitude throughout the lowering operation. In other words, the operators would like to open the bucket when they empty it and then maintain the bucket open while it is lowered onto the pile for refilling. Genenally the operators like to lower the bucket at a very high speed, including speeds above the normal operating speeds of the motors or at speeds which would be termed hypersynchronous speeds when wound rotor motors areused to drive the holding line and closing line-drums. It is well recognized that to maintain the bucket in the open attitude during its lowering at hypersynchronous speeds, as well as at other speeds, the controls of the motors must be so arranged that the motors are operated at speeds which will keep United States Patent 2,920,776 Patented Jan. 12, 1960 the bucket open. In the prior devices wherein each motor had its own independent control and its own master switch, this meant that the operator had to carefully manipulate both master switches to keep the bucket in the open attitude. If one motor tended to run faster than the other motor there was the additional problem of trying to regulate the speeds of the motors to obtain the desired results. This problem was often unsurmountable if the load on one of the lines was an overhauling load which would run one motor at a hypersynchronous speed. In such cases it was almost impossible to make the motors cooperate with each other and run at the same speed since there was no means to directly tie the drums or the rotors together to cause them to operate at the same speed in the lowering direction to hold the bucket in the desired single attitude (generally open) throughout the lowering of the bucket into the pile of material. It is thus apparent that one of the objects of the present invention is to provide a control system which overcomes the aforementioned problems and deficiencies in the prior control systems.

Another object of the present invention is to provide an electromagnetic clutch interconnecting the holding line and closing line motors and a control device for controlling the clutch in such manner that the rotors of the two'motors rotate together during lowering of the bucket onto a pile of material to maintain the bucket in a single desired attitude during such lowering thereof.

Another object of the present invention is to provide apparatus to tie the rotors of two motors together when they have accelerated to a predetermined speed so that they will rotate simultaneously at speeds above the predetermined speed to lower the load while maintaining the load in a single attitude.

A further object of the invention is to provide a new, useful, and novel control having a single master switch for a two line bucket hoist wherein the two motors are operable independently and/ or cooperatively to (1) close a bucket, (2) hoist the closed bucket, (3) empty the bucket and (4) lower the open bucket onto a pile of material while maintaining the bucket open.

A still further object of the invention is to provide a manually operable control means for completely controlling the hoisting, lowering, and attitude of a load, the control means including a multi-position controller and a switch interconnected with the controller for energizing two electric motors and an electromagnetic clutch cooperatively joining the motors.

A still further object of the invention is to provide a control for a two line hoist which is positive in operation, quick in response, and easy to operate.

Further objects and a fuller understanding of the invention will become apparent from the following descriptron of a specific example incorporating the invention and the attached claims directed to the invention, taken in conjunction with the accompanying drawings in which Figures 1, 2, and 3 compositely illustrate a control system for the holding line and closing line motors of a two line bucket hoist, the system including an electromagnetic clutch and a single master switch controlling the clutch and motors.

In the following description, the Figures 1, 2 and 3 will be treated as a single drawing since they compositely illustrate the circuit diagram of a control system which may be used to control a two line bucket hoist incorporating the features of the present invention. It is understood that the present illustration is for the purpose of exemplification and is not intended in any way to limit the scope of the invention either to the specific application illustrated or to the functions obtained thereby. Insofar as possible the relays are illustrated with the relay coils represented byavcircle and the contacts operated thereby are represented by parallel lines. The individual sets of contacts and their Operating coils are identified in the drawings either by letters or a combination of letters and numbers with the reference toarespective coil or; contacts being identified by the reference of the other plus a sufiix. It is further noted that wherelconvenient the letters used as reference characters or identification for a relay coilor relay contacts are to some extent an abbreviation of the function performed by the respective relay in the control system.

-In the specific example illustrated in the drawings a two line bucket 11 is adapted to be lowered towards and ra sed from a pile of material 11. As symbolically illustrated, the bucket is of the clam shell type supported by a closing line 12 attached to the hinge portion of the bucket 10 and wound on a holding line-drum 13, and a holding line 14 attached to one of the shells of the bucket at a distance from the hinge and woundon a holding line. drum 15. The closing line drum 13 is mechanically interconnected, as indicated by the dash-dot lines 16, to a rotor 17 of a closing line motor CLM and a brake 18. Similarly, the drum is mechanically interconnected as indicated by the dash-dot lines 19 to a rotor of a holding line motor HLM and a brake 2 1; Interconnecting the rotors 17 and 20 or drums 13 and 15'isan electromagnetic clutch 22,-the mechanical connections for which are illustrated in dash-dot lines 23 and 24 which interconnect the clutch 22 with the mechanical linkages 16 and 19, respectively. In the illustrative example, the motors are polyphase induction type motors with respective acceleration controls and with wound rotors constituting secondaries, and with stators constituting primaries con-. nectable to a source through the well known forward and reversing switches. I

.' The holding line motor, HLM has its primary side energizedfrom the'lines L1, L2 and L3 of a threephase power supply, the line L1 and L2 including main contacts HM1 and HM2, respectively, of a main contactor and the lines L2 and L3 containing hoist contacts HH1 and HH2, respectively, of a hoist contactor. Electrically interconnected with the hoist contacts HH1 and HH2 are reversing or lowering contacts HLl and HL2" to provide reversing of the direction of rotation of the rotor 20 by opening the contacts HH1 and HH2 and closing the contacts HLl and HL2 or vice versa.

. The brake 21 is of,a standard type spring applied, electrically released brake, normally used in hoist applications wherein the brake sets andprevents rotation 'of the rotor so long as the brake is de-energized and wherein the brake releases the rotor 20 for rotation so long as the brake 21 is energized. 'The brake 21 is therefore connected across the line L2 and L3 by suitable wires 121 so that the brake will be energized Whenever the primary or stator of the holding line motor HLM is energized.

The wound rotor 20 of motor HLM is provided with accelerating resistors, one for each phase, connected in such manner that one end of each resistor is connected to its respective end of the rotors phase'windin gs and the opposite ends of the resistors are electrically connected together. The eifective resistance value of the accelerating resistors is changed in the well known and customary manner by providing a plurality'of holding line motor acceleration contacts H1A1, H1A2, H2A1, H2A2, H3A1, H3A2, H4A1, H4A2, H5A1, H5'A2, H6A1'and H6A2 which interconnect the accelerating resistors at various points along theresistors, and in such manner that part of the resistors are shunted by the contacts when they are closed. Connected in shunt" with at least a major portion of one ofthe accelerating resistors is a .series circuit including relay coil HOS of an over'spe'edrelay and a capacitor 26. In shunt with themajor portion of the accelerating resistor is a series circuit including" an accelerating relay coil HSAR and a condenser 28. The accelerating resistor is at. least partially shunted by a series circuit including a relay coil HGAR and a 0011-.

denser 29. Finally, at least a major portion of the accelerating resistor is shunted "by a series circuit including a non-hoist relay coil HNH, an inductor 30 and a set of normally open contacts HH3 of the hoist contactor, and which are closed upon energization of hoist contactor coil HH. Shunting the HNH' coil is a condenser 31 and shunting the inductor '30'is a condenser 32.

The closing line motor CLM has its primary side ener: gized from the lines L1, L2 and L3 of a three-phase power supply, the lines Lland L2 including main contacts CMl and CMZ, respectively, of a main contactor and the line'sLZ and'LScontaining hoist contacts CH1 and CH2, respectively, of a hoist contactor. nected with the hoist contacts CH1 and CH2 are reversing or lowering contacts 'CL1 and CL2 to provide reversing of the direction of rotation of the rotor 17 by opening the contacts CH1 and CH2 and closing the contacts CLl and CL2, or vice versa.

The brake 18 is the same as orsimilar to brake Hand is connected across the lines L2'and L3 by suitable wires 118 so that the brake will be energizedwhenever'the primary orstator of the closing line motor is energized.

The wound rotor -17 of motor CLM is provided with accelerating resistors, one for each phase, connected in such'mann'er' that one end of each resistor is connected to its respective end of the rotors phase windings and the opposite ends of the resistors are electrically connected together. The effective resistance value of the ac celerating resistors is changedinwell known'and customary manner by. providing a plurality of closing line motor acceleration contacts C1A1, C1A2, C2A1, CZAZ,

C3A1, C3A2, C4A1, C4A2, C6A1 and C6A2, which interconnect the accelerating resistors at various points along the resistors and in such a manner that part of the resistors are shunted by the contacts when they are closed.

Connected in shunt with at least a major portion of one of the accelerating resistors is a series circuit including'a relay coil COX of an overspeed relay and a condenser 26. In shunt with the major portion of the same accelerating resistor is a series circuit including an accelerating relay'coil C4AR' and condenser 27. In shunt with the major portion of the accelerating resistor is a series circuit including an accelerating relay coil CSAR and a condenser 28. -The'accelerating resistor is at least partially shunted by a series circuit including an accelerating relay coil C6AR and a condenser 29. Finally, at least a major portion of the accelerating resistor is shuntedby a series circuitincluding a non-hoist relay coil CNH, an inductor 30', and a set of normally open contacts CH3 of the hoist conductor and which are closed upon energization of hoist contactor CH. Shunting the CNH coil is a condenser 33; and shunting the inductor 30 is 1 a condenser '34. t

The electromagnetic clutch 22 is electrically energized through a set of contacts CC1 of a clutch control relay having a relay coil CC, a full wave rectifier RECT, and a tran'sformer'TRQthe primary of which is connected across one phase of the incoming now'er, particularly lines" L1 and L2. When the contacts CC1 are closed, the clutch is energized to efiectively tie the rotor 17 with rotor 20,'and thus drum 1.3 with drum 15 so that the drums rotate at' a' speed in the same or in a desired direction relative toeach'other whereby lines 12 and Marc paid outat a speed in which the load or bucket will maintain a single attitude during'the lowering thereof.

The remainder I ofthe control system for carryingout the present. invention comprises a master switch MS and a plurality of relays, eachhaving relay contacts and an operating coil. The master switch MS and the relays which complete the control circuit are interconnected between'control energiz'ation' lines- 4-0 and 41, the linew'40 being electrically connected to-the power line L2, and the L3. The '"multi-position reversing master #SWitCh MS Electrically interconhas contacts 45 to 60. inclusive with one side of each set of contacts connected to the line 40. The contacts 45, 48, 53, 56, and 57 are normally closed and the remaining contacts are normally open in the oil position. In this instance a master switch having an off position and five hoist and five lowering positions is illustrated. In the first position hoist contacts 49, 50, 52 and 54 are closed. In the second position, hoist contacts 49, 50, 52, 54, and 55 are closed. In the third position, hoist contacts 49, 50, 52, 54, 55, and 57 are closed. In the fourth position, hoist contacts 49, 50, 52, 54, 55, 57, and

I 58 are closed, and in the fifth position contacts 49, 50,

52, 54, 55, 57, 58, and 59 are closed. When the master switch is moved to the first position lower, only the contacts 47, 48, 53, 56, and 57 are closed. In the second position lower, contacts 47, 48, 53, and 56 are closed. In the third position lower, contacts 47 and 48 are closed, while in the fourth position lower, the contacts 46, 47, 48, and 51 are closed, and finally, in the fifth position lower, the contacts 46, 47, 48, 51, and contact 60 are closed. When the master controller is in one of the hoist or lower positions, closure of a contact is indicated in the drawings by a cross aligned with the respective contact and the respective position. The

master switch MS is preferably of the standard and well known drum or cam type controller and necessarily has an operating handle (not shown). The structure of the handle and the master switch has not been detailed since such type master switches are commonly used in the industry.

To insure operation and energization of the motors HLM and CLM and the control system only when there is suflicient voltage in the power lines L1, L2, and L3, there is provided an undervoltage relay including undervoltage relay coil HUV and the respective normally open contacts HUVl. (The contacts HUVl are inserted in series in the line 40 between the connection of the master controller contacts 45 to the line 40 and the connection of the master controller contacts 46 to the line 40. The operating coil HUV is inserted in series with the contacts 45 and a normally closed hoist limit switch HLS and across the lines 40 and 41. Since contacts 45 are open when the master switch is in any of the hoist and lowering positions, a wire 61 interlocks the contacts 45 and the contacts HUVl so that power is continued to the relay coil HUV after the contacts HUVl have been closed and the master switch is moved from the off position to any of the hoist or lower positions. Shunting the hoist limit switch HLS are normally closed holding line motor hoist contacts HH4, which are operated with the hoist contactors HHl and HH2.

Connected in series with the master switch contacts 46 and between the lines 40 and 41 are relay contacts H6A3, relay contacts C6A3, and the clutch control coil CC. Shunting the clutch control relay coil CC is a time delay relay coil CTDR. Connected in series with the master switch contacts 47 and between the lines 40 and 41 are holding linemotor normally open lowering contacts HL3, normally closed non-hoist contacts HNHl, closing line motor normally closed non-hoist contacts CNHI, a contra-torque relay operating coil HCTR and the aforementioned normally closed holding line motor .hoist contactor contacts HH4. A normally closed clutch limit switch CLS is electrically interconnected from a point between the contacts HL3 and the contacts HNHI to a point between the contacts C6A3 and the coil CC. Forpurposes of description, the point or portion of the circuit between the contra-torque relay coil HCTR and the hoist contactor contacts HH4 will be given reference character 62.

Interconnected in series with the normally closed master switch contacts 48 and between the line 40 and the electrical connection 62 are contra-torque open con- .tacts HCTRI and HCTR2, and normally closed hoist holding line motor acceleration relay coil HlA. It is noted that electrically the point of connection between the contacts HL3 and HNHl and the point of connection between the contacts HCTRI and HCTR2 is a single electrical point. Shunting the normally closed contacts HHRl and the H1A relay operating coil are contacts H1A3 in series with holding line motor main contactor operating coil HM. Shunting the normally open contacts H1A3 are normally closed digging limit switch contacts DLS. Continuing the design of the circuit, it is noted that the off position open master switch contacts 49 are connected in series with normally closed digging relay contacts HDRI, the limit switch DLS and the operating coil HM and between the line 40 and the point 62.

Shunting the relay contacts HCTRl, HCTRZ, HHRI, and relay coil HlA are normally open digging relay contacts HDR2, normally open closing line motor lowering contactor contacts CL3, normally closed non-hoist relay contacts CNH2, normally closed non-hoist relay contacts HNH2, and time delay relay coil CCT R. Shunt ing the contacts HDR2 and CL3 are normally open time delay relay contacts CCTRI and shunting the contacts CNH2, contacts HNH2, and the coil CCTR are time dolay relay contacts CCTR2 and closing line motor main contactor coil CM. A wire 63 also connects the electrical point between the switch contacts 47 and the contacts HL3 with a point between the contacts HDR2 and the contacts CL3. Also normally open clutch control relay contacts CC2 are interconnected from a point between the contacts C6A3 and the coil CC to a point between the contacts CL3 and CNH2. The master switch contacts 50 are interconnected between the line 40 and apoint between the contacts CCTR2 and the coil CM.

There is provided a pushbutton TB, which is normally open and which may be closed when desired to cause an opening of the bucket 10. The pushbutton TB is connected in series with contra-torque relay contacts HCTR3 and digging relay coil HDR between the lines 40 and 41. There is also provided a button type switch HB which is normally positioned in the control handle of the master switch MS and which may be closed for causing the bucket to open to empty itself. This button switch HE is connected in series with normally closed contacts HCTR4 and a hoist holding relay operating coil HHR and between the lines 40 and 41. The master switch contacts 51 are connected in series with normally open lowering relay contacts HLRI, normally closed hoist contactor contacts HHS and lowering contactor operating coil HL between the lines 40 and 41. Shunting the contacts HLRI, contacts HHS and coil HL are normally closed digging relay contacts HDR3, normally closed hoist holding relay contacts HHR2, and lowering relay coil HLR, all of which are connected in series. Similarly, lowering contactor normally open contacts CLRl, hoist contactor contacts CH4, and lowering contactor coil CL, all of which are connected in series, shunt the series including contacts HLRI, HHS, and coil HL. A lowering relay operating coil CLR is further connected in shunt with the contacts HLRI, contacts HHS and the coil HL.

The master switch contacts 52 are connected in series with normally closed holding line motor lowering contactor contacts HL4 and hoist contactor coil HH between the lines 40 and 41. Shunting the master switch contacts 52 are normally closed lowering relay contacts HLRZ and normally open contra-torque contacts HCTRS and normally open main contactor contacts HMS. There is further interconnected in series and between the lines 40 and 41 normally closed lowering relay contacts CLR2, normally open contra-torque relay contacts CCT R3, normally open main contactor contacts 0M3, normally closed lowering contactor contacts CL3, and the hoist contactor coil CH. Connected in series with the master switch contacts 53 are normally open contra-torque relay contacts H2CR1 and the acceleration contactor coil CIA. The master switch contacts 54 shunt the series connection 'It isf also'noted that-a set of contacts HDR4 interconnect a point betweenthe switch contacts 53 and'the relay contacts-" CCTR4, and a point between the' switch contacts 51 and the lowering relay coil CLR. The drawing further illustrates normally open timing relay contacts CTRI, ove'r speed relay contacts H081 and C081 which are connected in. parallel-with each other and from a point between the switch contacts 54 and the relay contactSI-IZCRI to a point between the contacts CM3 and C133. "Normally open lowering contactor contacts GL4 shunt the m'aster switch contacts 54 and normally open control relay contacts H1CR1 shunt the contacts H2CR-1. The master switch contacts 55 are connected in series "wit-h normally'open main contactor contacts HM4 and an accelerating contactor coil HZA and between the liiies"40 and41. Shun'ting the master switch contacts 55 are normally open lowering contacts HLS. Also shuntin'g'the series -connecti'on of the contacts 55 and HM4 are the 'cohtac'ts 52 and relay contacts HOSZ, the contaCtSHOSZ in turn being shunted by relay contacts C052. -'The' normally closed masterswitch contacts 56 are-connectedin series-with normally open contra-torque relay contacts HCTRG, normally closed contra-torque relay contacts CCTRS, normally-open main. contactor contacts CM4,'-'and--acceleration contactor coil CZA, all, of which are iiiterconnectedbetween the lines '40 and-41. In addinon, the master switch contacts 55shunt the master switch contacts56 and the normally closed contacts HCTR6. *The masterswitch contacts '57 are connected in series withthe-acceleration'contactor contact H2A3 and the acceleration contactor coil H3A and between the lines 40*ancl 4'1. Shunting the contacts H2A3 and the coil is a series circuit including normally closed contratorquerelaycontacts CCTR6, normally open acceleration contactor contacts -C2-A3, and the acceleration contactor coil= CSA. Lowering relay contacts HLR3 shunt the master switch'co'ntacts 57.

The master-switch contacts 58 are connected in series withl'no'rmally closed accelerating relay contacts H4AR1, normally closed control relay contacts HZCRZ, and the acceleration contactor coil H4A. Shunting the master switch cont-actsSS areno'rmally open lowering relay contacts HLR l, and shunting the contacts I-I4AR1 and HZ'GR'Z are thenormally open control relay contacts HICRZ. Also shunting the relay contacts H4AR1, HQGRZ and 'the coil -H4A arenormally closed acceleration relay contacts-C4ARi1 and acceleration contactor coil 64A.

'The'mas'ter' switch contacts 59 are connected in series with nonnallyclo-sed acceleration relay contacts HSARI and acceleration contactor coil I-ISA, and between the lines 40and-41. "shunting the relay contacts HSARl and the coil 'HSA are a plurality of shunt circuits, one er which comprises acceleration relay contacts CSAR] and'the acceleration contactor coil CSA, another of which comprises the acceleration relay contacts H6AR1 and an acceleration contactor coil H6A, and a third of which comprises norm-ally'open control relay contacts H1CR3, normally open control relay contacts I-I2CR3, and control relay coil HlCR. -"Shunting the contacts C5AR1 and the coil CSA' "are normally closed time delay relay contacts CTDRI, normally closed 1 accelerating relay contacts CGAR L' -and "the acceleration contactor coil C6A. In addition; acceleration relay contacts HSARZ shunt the contacts H 1CR3, and normally open accelerating relay contacts C5AR2 alsoshunt the contacts H1CR3. It is noted that a'set'ofnormally open lowering relay contacts "shuntthe' master switch contacts 59.

' This-part of the control circuit is completed by includingin cooperative arrangement'with the aforementioned coils and -contacts,"lowerin'g relay contacts CLR3, CLR4,

' (-3-LR6,- andcont'ra torque relay contacts CCTR7 I Th'ecoiitacts are connected-between the line and a point betweenttheicontactsr CCTR5,1and thel contacts CM4 which1are connected in -serieswith theitmaster switchcontacts. 56. The normally: opencontra-torque contacts CCTR7 are connected to a point between the master switch contacts 57 and 'the switch contacts H2A3 and '-the aforementioned point between the contacts CCTRS and the contacts CM4, which were'in series with the master switch. contacts 56. The contacts CLR4are connected in shunt withnthecontacts' 57 of the master switch MS and the'relay contacts CCTR6. Similarlythe contacts CLRS are connected in shunt withlthe master switch contacts 58 and the contacts CLR6 are connected in shunt with the master switch 59.

The system is completed by connecting the normally 'open master switch contact 60 in series with time delay relay contacts CTDR2 and control relay coil H2CR and between the lines 40 and 41.

'Having thus described the physical'construction of the circuit and the relays 'and contactorsand master switch used herein, as well as the electromagnetic clutch and motors, the operation .of 'the'circuit will now be :described.

Operation The operation of the system is best understood :by starting with the bucket 10 open and resting on the material' pile 11 and with the master switch MS in the Off point. The digging limit switch-DLS is closed when the bucket 10 is at :the pile of material 11, or what is called the digging zone. The undervoltage relay coil HUV' is energized by closed master switch contacts. 45 to close its contacts HUVI, which establish a circuit through wire- 61 and around contacts 45. Moving the master switch MS to the first point hoist and closing the push-buttonI-IB :in the hoist handle energizes the contact'or coils CM, CH, and CIA to close their respective contacts CM1, CM2, CM3, CM4, CH1, CH2, CH3, C1A1 and ClAZ to give a relatively large (normally torque on the-closing line motor CLM which will then start closing the bucket 10 by its rotor-v17 turning drum 13 to reel infline 12. The closing line motor .CLM- is accelerated by the successive closing of contacts CZAI, CZAZ, C3A1, C3A2, C4A1, C4A2, CSAl, CSAZ, C6A1 and C6A2 in accordance with normal well known procedures for accelerating wound-rotor type motors.

At this same time, contactorcoils HM,.HH, and relay HHR (controlled by push button HB) are also energized, causing coil HM to close contacts HMl, HM2, HMS, and HM4, causing coil HH to close contacts HHI, HHZ, H113, and open contacts HH4 and HHS, and causing'coil HHR to opencontacts HHR1 and HHRZ. Opening of contacts HHR1 prevents energization of acceleration contactor coil HlA, thereby holding acceleration contacts H1A1, H1A2, and H1A3 open. In remaining open, the acceleration contacts I-I1A2 prevent the energizationiof acceleration contactor coils H2A, HSA, H4A, HSA, and H6A and thus prevents acceleration of the motor HLM. This gives a very small (usually 10%) torque to the holding line motor HLM toallow thebucketli) to settle while digging and without allowing cable or line 14' to become slack.

If the bucket 10 starts to .tip over during digging, the holding line motor HLM can be stopped to stop rotation of rotor 20 andvdrum 15' by closing the pushbuttonrTB, which is usually placed in one of the handleslof the trolley operating controls (not shown). Closing pushbutton TB causes energization of coil HDR, .thereby opening contacts HDRll and effecting de-energization of contactor coil .HM to open contacts HMl .andHMZ. vWith and opened 1 thus" restoring the normal 1 bucket closing 'op e'ration "and circuits under the control-of masterswitch MS andbuttortI-IB. I

When the bucket is closed, i.e.reaches its closed attitude, the pushbutton HE is released and opened, deenergizing hoist holding relay coil HHR and thereby closing hoist holding relay contacts HHRl, thereby energizing acceleration contactor coil H1A 'which closes contacts H1A1 and H1A2. This permits the remaining accelerating contactors for the holding line motor HLM to be operated in the well known manner, the same as the closing line motor CLM. The bucket 10 will then be hoisted with both motors HLM and CLM sharing the load of the filled bucket, until either the hoist limit switch HLS is tripped, or the master switch MS is moved to the Off, point.

To open the bucket, the master switch MS is moved to the fourth point lower and the pushbutton HB in the hoist master switch handle is closed. The master switch contacts S1 are closed in the fourth point lower to efiect energization of lowering relay coil CLR, the closing of its contacts CLRI to energize lowering coil CL, whereupon normally open contacts CL1, CL2 and CL3 close. Upon closure of contacts CL3, contra-torque relay coil CCTR is energized through normally closed contacts CNH2 and HNH2 and master switch contacts 47. Energizing coil CCTR closes contra-torque relay contacts CCTRI and CCTRZ, thereby energizing main-contactor coil CM to close contacts CMl and CM2 in lines L1 and L2. At this same time, the lowering relay coil CLR is energized through master switch contacts 51 to close contacts CLRI and energize lowering contactor coil C1, which, in turn, closes contacts CLl and CL2. Closure of contacts CM1, CM2, CL1 and CL2 connects motor CLM to lines L1, L2, and L3 releases brake 18 and cause rotation of rotor 17 in the lowering direction. Also closure of contacts CL4 and CLR3 permit energization of acceleration contactor coils CIA and 02A and acceleration of the rotor in a normal manner so that it will rotate drum 13 in a direction to pay out line 12 and open bucket 10. During this time, the holding line motor HLM is held still by brake 21 and hoist holding relay contacts HHR2 (coil HHR being maintained energized by the pushbutton HB in the hoist master switch handle) being open, thereby keeping lowering relay coil HLR deenergized' So long as coil HLR is de-energized, its contacts HLRl prevent closing of contacts HL1 and HLZ by preventing energization of lowering contactor coil HL and this prevents energization of motor HLM.

After the bucket reaches its open attitude, the operator releases and thus opens the pushbutton HB, effectively de-energizing the hoist holding relay coil HHR which, in turn, allows the contacts HHR1 and HHR2 to close. When contacts HHR2 close, a circuit is established through master switch contacts 51 and normally closed contacts HDR3 to energize lowering relay coil HLR which, in turn, closes contacts HLRl to energize lowering contactor coil HL and thereby close contacts HL1, HL2, and HLS and open contacts HL4. With contacts HL3 now closed, a circuit is established through master switch contacts 47 to energize contra-torque relay coil I-ICTR which, in turn, closes contra-torque contacts HCTRI and 'HCTRZ. This establishes a circuit through the master switch contacts 48, contacts HCTRI, HCTR2, normally closed contacts HHRl, and acceleration contactor coil HlA, to energize the coil HlA. Energization of coil HlA effects a closure of contacts H1A1, H1A2, and HlA-S with the contact I-I1A3 establishing energization of the main contactor coil HM. Upon energization of the main contactor coil HM, the main contacts HMl and HM2 are closed, whereupon the brake 21 is released and the holding line motor HLM energized so that its rotor 20 rotates drum 15 in the lowering direction to pay out line 14. Since the contacts HLS, HLR3, HLR4, and HLRS are also now closed, the holding line motor HLM accelerates to full speed in the lowering direction upon --se'quential energization of the accelerating contactors HZA, H3A, H4A, HSA, and H6A.

When the accelerator contacts close, a circuit is established through master switch contacts 46 to energize the clutch control relay coil CC, which closes contacts CCl to energize clutch 22 and tie the two motors HLM and CLM together. Timing relay coil CTDR is also energized when coil CC is energized and after a brief (usually /2 second) time delay, the normally closed contacts CTDRl open and de-energize acceleration contactor coil C6A. The time delay permits the magnetic clutch 22 to build up to its maximum torque. The de-energizing of acceleration contactor coil C6A reduces the regenerative torque of the closing line motor CLM. This limits the torque transmitted through the magnetic clutch to a maximum value (usually within the 50% of full load torque of one motor). The bucket will then be lowering with the two motors synchronized at a speed which, due to the weight of the bucket 10, is slightly higher than synchronous speed, and with clutch 22 maintaining the bucket in a single attitude (in this instance open).

Moving the master switch MS to fifth point lower causes contacts 60 to energize control relay coil HZCR and effect the closing of the contacts H2CR3 and opening of contacts H2CR1 and H2CR2. Opening contacts H2CR2 de-energizes contactor coil H4A, and opening contacts H2CR1 de-energizes contactor coil CIA. With contactor coils H4A and CIA de-energized, coils HSA, H6A, CZA, C3A, C4A, CSA, and C6A will become deenergized and the respective acceleration contacts will open to effectively increase the accelerating resistors to their larger resistance value. This will cause the motors HLM and CLM to rotate at hyper-synchronous speed in the lowering direction, usually at about speed of the motors, thereby rapidly lowering the bucket 10 towards pile 11 with clutch 22 maintaining the bucket in a single attitude. It is also noted that the closure of relay contacts H2CR3 also establishes a circuit for energizing the control relay coil HICR. If overspeeding occurs, the frequency responsive accelerating relays HSAR and CSAR are energized to close their contacts H5AR2 and C5AR2 to energize the relay coil HICR. The energization of control relay coil HlCR closes contacts H1CR1, H1CR2, and H1CR3 to return the motors HLM and CLM to synchronous speed in event the bucket 10 overspeeds during lowering. Contacts H1CR1 and H1CR2 then close andenergize the accelerating contactors CIA and H4A and close contacts ClAl, C1A2, H4A1, and H4A2, respectively, to slow the bucket 10 down and return the motors to synchronous speed. De-celeration of the motors is controlled through the frequency responsive acceleration relays H4AR, HSAR, H6AR, C4AR, CSAR, and C6AR. The relay coil HlCR is then maintained energized through its own contacts H1CR3, and the motors remain near synchronous speed for the rest of the lowering cycle. This is desirable since an overload condition is indicated, and the control is prevented from oscillating between slowing down and overspeeding.

When the bucket approaches the material pile, and assuming that the master switch is in the fifth point lower without an overspeed condition existing, slowing down is achieved by moving the master switch back to fourth point lower, which de-energizes relay coil H2CR by the opening of the master switch contacts 60. De-energizing coil H2CR opens contacts H2CR1, H2CR2, and closes contacts H2CR3 to energize coil HlCR and return the motors to synchronous speed in the same manner as explained for an overspeed condition. Moving the master switch back to third point lower applies counter torque to supply stronger braking of both motors. This is accomplished by the de-energization of the lowering relay and contactor coils HLR, CLR, HL and CL through the opening of master switch contact 51. Contacts HLRl, HLR3, HLR4, HLRS, CLRI, CLR3, CLR4, CLR5, CLR6, HL1, HL2, HL3, HLS, CL1, CL2, and CL4 are thus returned to open position, and contacts HLR2, CLR2, HL4, CL3 are returned to-closed position.- Also 11 iz'r'equencyrresponsiven relay :coils 'H4AR,: HAR,-. H6AR, Q4AR,1 .GSAR, .and C6AR respond to .allow r their. con- ,tacts H4AR1, :.I-I5AR1, PH6AR1, C4AR1, -.C5AR1 and EGARI to open,athereby de-energizing acceleration contactor coils' H4A,H5A, 'H6A, (24A, CSA and C6A. Upon:closing ofcontacts vHL4 and CLRZ, CCTR3 and .CM3, the..contactor. coils HH and CH .are energized to .close contacts 'HHI, HH2, .CHLand CH2, respectively, to energize motors HLM and CLM in a hoisting direction. :At this time, relay coils. HCTR. and CCTR remain. energizedathrough their own contacts'HCTRZ and CCTRZ. .Contac'tor. coils HM and CM remain energized by.icurrent flow-through contacts HCTR2 and CCTRZ. Hoisting power is now applied to both' motors I-ILM- and .CLM with. contactor coil HlA'energized and accelera- :fiOIl contactsHlAl and HIAZ. on the holding line motor HLM clo'sed, and-with I all accelerator contactson the :closingfline motor .CLM. open. This will slow the bucket to a slowspeed, usually:approximately %of its-Isynchronous speed.

Moving the master switch MS tosecond point. lower willetfectenergization 0f contactor coils HlA and CIA,

thereby closing I acceleration contacts HlAl, -H1A2, Q1A1,.and C1A2-to increaseithe braking torques for a faster slowdown. The torque on this point should be .suflicient'to stop the movement of the bucket towards the pile, however faster-torque braking may be' obtained by. moving the. master switch to first point lower, effecfoively. energizing contactor. coils HSA and (32A and thereby closing contacts H3A1, H3A2, CZAI, and CZAZ to provide: the strongest counter torque for fast stops. 'If itheoperatorl sees that he isygoing to stop short of the -pile,:hecan move themaster switch -back to .third point lowerywhich willallow the bucket to'slowly lower "onto 'theipile. I

."In' event thermaster switch is pulled to the Offpoint lquicklyxzfromone of the lower points, the motors will have .counter torque applied-and will bring themselves aoa stopbefore setting of the magnetic brakes '18'and 21. Thisis accomplished by :the non-hoist relay-coils'HNH .a'ndI CNHremaining inoperative so long as the rotors are turning. Thenormallyclosed :contacts HNHI, HNHZ, CNHI andCNHZ, in circuit with coils HCTR and CCTR, remain closed until the rotors 17 and 20 are at a virtual standstill, at which timercoils H-NH and CNH become energized and contacts ZHNHl, HNHZ, CNHl, and -CNH2 open. It isalso noted that the clutch control relaylcoilLCC is also energized so long as the non-hoist :relay contacts HNHI: and CNHl are closed to insure the bucket remaining in the open attitude as the motors :HLM and CLM stop.

For the operators convenience, the bucketcan also be EOPEHedbY-USC of the pushbutton TB, which is usually placed in the master switch of the controls for atrolley used to transport -the buckethorizontally away from the pile. As the bucket runs over a hopper or other place of depositing the contents thereof, depressing and closing the pushbutton TB opens the bucket 10, providing master switch MS is in the off, .first or second point lower posi- .tions. In these positions, the hoist master switch MS has :no effect since the control is :inoperative.

'When the pushbutton TB is closed, the relay coil HDR lisenergized and contactsHDRZ and HDR4 are closed, ienergizing the relay coil CLR which effects the energizationof the closing line: motor CLM and-:thus' the "openingof the bucket in a :manner as previously described. Also, closing contact HDRZenergizes the relay coilCCTR andthe contactor coil CM, thereby permitting \the lowering sequence to be completed. At this same :time, the relay contacts 'HDR3 are open to keep the relay .coil HL-R :from being energized ttoprevent the holding'line .from running.

while in the. embodimentiof the present invention. dis- Iclos'ed forthe purposes-of illustration, alterna'tingcurrent .po1yphase induction motors are used, obviously other .types of. motors-can? be substituted therefor withoutfdeload at a predetermined attitude relative to the mass during the lowering thereof towards the mass, said device comprising, a first motor provided with a rotor for paying out the first line, a second motor provided'with a rotor for paying out the second line, energizing means for selectively energizing said motors independently of each other, first means in circuit withsaid energizing means and operable to cause said energizing means to rotate the rotor of said first motor in a lowering direction to pay out the first line, second means in circuit with said energizing means and operable to cause said energizing means to rotate the rotor of? said second motor ina lowering direction to payout the second line, a'first acceleration con- 'trol in circuit with saidfirst motor to accelerate the rotor of the first motor to av predetermined speed and independently of said second motor, a second acceleration control -in circuit with said second. motor to accelerate the rotor inter-associating the rotors of said first and second motors and energizable to clutch the rotors together for rotation together and deenergizable to unclutch the rotors so that one rotor may rotate independently of the other rotor, and circuit means responsive to said firstand second acceleration controls to energize said clutch upon the rotors reaching said predetermined speed of rotation in the lowering direction to cause the rotors to rotate together in said lowering direction whereby the first-and second lines are simultaneously paid out to lower the load while maintaining the load in a single attitude throughout the loweringthereof.

2. The structure as defined in claim 1 whereinsaid rotors are wound rotors and said acceleration controls are in circuit with their respective ones of said rotors.

3. The structure of claim 2 wherein each of said acceleration controls include acceleration resistors and said circuit means includes a frequency responsive relay for each rotor, each said relay having a frequency responsive coil in circuit with its respective resistor and relay contacts in said circuit means.

4. A material handling device comprising spaced first and: second lines, a first motor provided with a wound rotor for paying out the first line, and a secondmotor provided with a wound rotor for paying out the second line, abucket suspended by said lines and responsive to movement of one of said lines relative to the other of said lines to attain various attitudes including an open attitude in which the bucket willdig into a pile of material and a. closed attitudev in which the bucket will carry material from said pile of. material, said bucket having a bucket weight sufiicient to overhaul said motors and cause the rotors to rotate. at speeds above predetermined speeds of the motors during lowering of the bucket onto a pile of material, energizing means for selectively energizing said motors independently of each other, first means in circuit with said energizing means andoperable ;.to cause said energizing means to rotate the rotor .of said 'first motor in a lowering direction to pay out thefirst line, second means in circuit with said energizingmeans and operable to cause said energizing means to rotate the rotor of said second motor in a lowering. direction .to pay out the second line, a'first acceleration control in circuit with the wound rotor of said firstv motor to accelerate the first motor to.a predetermined. speed and independently of. said. second .motor, a second acceleration controlin. circuit with the wound rotor of said second motor to accelerate the second. motor .to a predetermined speed and independently at said. first.motor,.-an.electrov 13 4 rna gne tic' clutch inter-associating the rotors and energizable toclutch the rotors together for rotation together and de-energizable to unclutch the rotors so that one rotor may rotate independently of the other rotor, and circuit -mean's' re'sponsive to said first and second acceleration 1 controls to energize said clutch upon the rotors of said motors reaching said predetermined speed of rotation in the lowering direction'to cause the rotors to rotate together in said lowering direction at speeds above said predetermined speed whereby the first and second lines are simultaneously payed out to lower the bucket while maintaining the bucket in a single attitude throughout the lowering thereof onto thetpile of material.

5; The structure as defined in claim 4 wherein the motors are alternating current motors and each of said acceleration controls "include acceleration resistors and said circuit means includes a frequency responsive relay for each rotor, each said relay having a frequency responsive coil in circuit with its respective resistor and relay contacts in said circuitmeans.

A material handling device comprising spaced first and second lines, a first induction motor provided with a woundrotor for winding in and paying out the first line, a second induction motorprovided with a wound rotor for :winding in and paying out the second line, a bucket suspended by said lines and responsive to movement of one of said lines..relative to the'other of said lines to attain various attitudes including an open attitude in which the bucket will dig into a pile of material and a closed attitude in which the bucketjwillcarry material from said pile of material, said bucket having a bucket weight sufficient to overhaul said motors and cause the rotors to f 'r'otate at speeds above the rated synchronous speeds of the motors during lowering of the bucket onto a pile of "material, energizing means for selectively energizing said motors independently of each other and with alternating cu'rrent,'-firs't means in circuit with said energizing means and operable to cause said energizing means to rotate the rotor of said first motor in a hoisting direction to wind in the first line and to rotate the rotor of said first motor in a lowering direction to pay out the first line, second means in circuit with said energizing means and operable to cause said energizing means to rotate the rotor of said second motor in a hoisting direction to wind in the second line and to rotate the rotor of said second motor in a lowering direction to pay out the second line, a first acceleration control in circuit with the wound rotor of said first motor to accelerate the first motor in both directions independently of said second motor, a

second acceleration control in circuit with the wound rotor of said second motor to accelerate the second motor in both directions independently of said first motor, a multi-position master controller inter-associated with said first and second means and said acceleration controls, said master controller being operative in a first of said positions to cause said first means to de-energize the first motor and said second means to energize the second motor to rotate the rotor thereof to wind in the second line while said first line remains relatively stationary to effect a closed bucket attitude, said master controller being operative in a second of said positions to cause said first and second means to energize said first and second motors to rotate the rotors thereof in said hoist direction to wind in the first and second lines to hoist the bucket while maintaining the bucket in said closed attitude, said master controller being operative in a third position to cause said first means to de-energize the first motor and said second means to energize the second motor to rotate the rotor of the second motor in the lowering direction to pay out the second line while said first line remains relatively stationary to change the bucket from said closed attitude to an open bucket attitude, said master controller being operative in a fourth position to cause said first and second means to energize said first and second motors to rotate the rotors thereof in said lower- 14 ing direction to pay out the first and second lines and lower the bucket, an electromagnetic clutch inter-associatin'g the rotors and energizable to clutch the rotors together fo-r'rotation together and de-energizable to unclutch the rotors so that one rotor may rotate independently of the other rotor, and circuit means responsive to said master control while said master control is in said fourth position and said acceleration controls to energize said clutch upon the rotors of said motors reaching a predetermined speed of rotation in the lowering direction to cause the rotors to thereafter rotate together in said lowering direction at speeds above said predetermined speed whereby the first and second lines are simultaneously payed out to lower the bucket while maintaining the bucket in a single attitude throughout the lowering thereof onto a pile of material.

7. The'structure as defined in claim 6 wherein each of said acceleration controls includes acceleration resistors and said circuit means includes a frequency responsive tion means in circuit with at least one of said acceleration resistors and said master controller and responsive to the speed of the rotors reaching a certain speed when said master controller is in said fourth position to effect an increase in the acceleration resistance to limit the speed of payout of the lines during lowering of the bucket when the bucket is overhauling the motors.

9. The structure as defined in claim 6 including a clutch limit switch means in said circuit means and operative while the bucket is in close proximity with the pile of material to keep the clutch energized while the master control is moved from one position to another position.

10. A material handling device comprising spaced first and second lines, a first induction motor provided with a wound rotor for winding in and paying out the first line, a second induction motor provided with a wound rotor for winding in and paying out the second line, a bucket suspended by said lines and responsive to movement of one of said lines relative to the other of said lines to attain various attitudes including an open attitude in which the bucket will dig into a pile of material and a closed attitude in which the bucket will carry material from said pile of material, said bucket having a bucket weight sufiicient to overhaul said motors and cause the rotors to rotate at speeds above the rated synchronous speeds of the motors during lowering of the bucket onto a pile of material, energizing means for selectively energizing said motors independently of each other and with alternating current, first means in circuit with said energizing means and operable to cause said energizing means to rotate the rotor of said first motor in a hoisting direction to wind in the first line and to rotate the rotor of said first motor in a lowering direction .to pay out the first line, second means in circuit with said energizing means and operable to cause said energizing means to rotate the rotor of said second motor in a hoisting direction to wind in the second line and to rotate the rotor of said second motor in a lowering direction to pay out the second line, a first acceleration control in circuit with the the wound rotor of said first motor to accelerate the first motor in both directions independently of said second motor, a second acceleration control in circuit with the wound rotor of said second motor to accelerate the second motor in both directions independently of said first motor, manually operable master control means includ- :operative when-said controller aisdn-a first of saidpositions to cause said firstnmeans to lde-energize the first vmotor and said second means to venergize the .second motor to rotate the rotor thereof to wind in the second line while said first line remains relatively stationary to effect a closed bucket attitude, said master control means being operative when said controller is in a second of rsaidpositions to causesaid first andisecond means to --energize said first and secondmotors to rotate the rotors ,thereof in said hoist direction to wind the first and second vlines to hoist the bucket while maintaining the bucket in 1 closed attitude, said master control means 'being operative --when said controller is in a third position and said switch ,is in operative position to cause, said first means to deaenergize the first motor and said-second meansto'enen.

gize the second motor to rotate the rotor of the second .motor in the lowering direction to pay out the'second line while said first line remains relatively. stationary to .change the bucket from said closed: attitude'to-an open :bucket attitude, said master control means: is operative: when said controller is in one of said positions-and said switch is in inoperative positiontogcausessaid firstand second means to energize said first andsecondmotors to rotate the rotors thereof 'insaid-lowering direction'to .pay out the first and second lines and lowerthebucket; an electromagnetic clutchinter-associating the rotors and energizable to clutch the rotors together. for rotation 'toigether and de-energizable to unclutch the rotorssothat one rotor may rotate independently of theuother; rotor,

1 and circuit means responsive to said master. controlrne'ans i and said acceleration controls when said master controller is in said one of said positions: andsaid switch is in said inoperative position to energize said clutch upon .the rotors of said motors reaching a predetermined speed of rotation in the lowering directionto cause the rotors to thereafter rotate together in said lowering direction at speeds above said predetermined speed-wherebythe first siverelay -for each -rotor,: each said' relay havinga :fre-

quency responsive coil incircuit with its-respective resistor and relay contacts insaid circuit'means.

; 512. The structure-as defined in claim 10 wherein: each .zof saidacceleration controls include acceleration resistors,

shunt means progressively shunting out-saidresistors :as

the speed of lthe respective rotors :increase; and deceleration'meansiin'circuitwithiatleast onerof sa'id acceleration resistors and saidmasterscontroller:and responsive :to the speed of. the. rotors: reaching; a; certain :speedmwhen ,said master controllenisein one:- of SaidI positions :and said switchisin saidxinoperativepositionto effect; am-increase in the acceleration resistanceio' limitithespeediofipayout ofl the lines during lowering of the bucket-"when :th

tucker is overhauling the motors.

1 13. l-The structure .as. defined iin claim l Twherein:

imotors are'wound rotormotors. v I

t 14. The structure as defined' in: claim 13 wherein the Wound rotormotors areinduction motors. I

' 115. .The structure -as defined in claimifi' zwherein the motors are induction motors. f

References Cited in the file of this patent IUNITED STATES PATENTS I structure as defined 'in :claim l0 wherein each 

